1. Field of the Invention
This invention relates to a cooling system for water-cooled internal combustion engines, particularly for boat motors, which system comprises a pump for circulating cooling water over a heat exchanger and through an expansion vessel, a raw water pump for maintaining a flow of raw water as a cooling fluid through the heat exchanger, a reservoir, and a pressure relief valve and a check valve which are connected in parallel between the expansion vessel and the reservoir.
2. Description of the Prior Art
In known cooling systems of that kind the reservoir constitutes an overflow vessel. When a temperature rise of the cooling water causes the pressure in the expansion vessel to rise above a predetermined value, water and/or steam will be displaced from the expansion vessel into the reservoir. On the other hand, water will flow back from the reservoir into the expansion vessel in response to a temperature drop of the cooling water. But it is generally desirable to operate the cooling water circuit under a high pressure because this will obviously increase the boiling point of the cooling water, which in that case can assume a higher temperature so that the heat exchanger and also the pump for raw water may be designed with smaller dimensions. Besides, the cavitation in the circulating pump and in the engine will be reduced and the higher temperature level will result in a higher efficiency of the engine. In the known system a higher pressure in the expansion vessel and in the entire cooling water circuit cannot reliably be achieved. This is due to the fact that when a high load on the engine has resulted in a temperature rise of the cooling water and a corresponding pressure rise in the expansion vessel and a corresponding quantity of cooling water has been displaced from the expansion vessel into the reservoir and if then a temperature drop occurs in the heat exchanger and/or in the expansion vessel for any reason whatever, cooling water will be sucked back from the reservoir into the expansion vessel and that operation will result in a high pressure drop in the expansion vessel. Such a pressure drop may also occur, for instance, if the quantity of water contained in the cooling circuit is inherently insufficient or if a leak occurs in the cooling circuit. In case of a leak which is so large that the quantity of cooling water decreases below a predetermined lower limit, the engine must be shut down if heavy damage to the internal engine is to be avoided. The failure of the motor a boat on the high seas may involve a high risk for the boat and its crew, particularly because it is very difficult to continually fill up the system with cooling water on a heavy sea.